1. Field of the Invention
The present invention relates generally to apparatus and methods for separating cellular material from biological fluids and, more particularly, to the design and use of a centrifugal rotor which is capable of separating plasma from an applied volume of whole blood and optionally distributing the plasma to a plurality of test wells within the rotor.
Blood tests frequently require that potentially-interfering cellular components of the blood be separated from the blood plasma prior to testing of the plasma. It is also frequently desirable to divide the separated blood plasma into a plurality of discrete aliquots so that a variety of tests or assays may be performed on the blood. Such separation and division steps have heretofore been typically performed by centrifugation to separate the blood plasma from the cellular components, followed by manual or automated pipetting of the blood plasma into separate test wells. Such procedures are labor intensive and time-consuming, and various automated systems and methods have been proposed for providing multiple aliquots of plasma suitable for testing in a more efficient manner.
Of particular interest to the present invention are centrifugal rotors which have been modified both to separate plasma from whole blood and to distribute the separated plasma into separate test wells. The use of such rotors can provide a plurality of discrete plasma volumes which may be tested or evaluated, all present within the centrifugal rotor, greatly enhancing the efficiency of automated testing procedures.
Although a significant improvement over prior manual or partly manual procedures, previous modified centrifugal rotors have suffered from a number of deficiencies. Such rotors have frequently required the application of relatively large volumes of whole blood in order to achieve the desired separation and distribution. The efficiency of separation has frequently been low, typically on the order of 5% based on the initial amount of plasma available. Moreover, such rotors have frequently utilized complex designs which are difficult and costly to manufacture. Often, the rotors require various separable parts or components which are brought together or separated at different points in the centrifugation procedure. Previous centrifugal rotors have often been limited in the number of discrete samples and test wells which they can provide, and in some cases require the use of a separate displacement fluid to effect flow of blood and plasma through the system.
For these reasons, it would be desirable to provide improved centrifugal rotors and methods suitable for separating blood into plasma and cellular components and for further distributing the separated plasma into a plurality of discrete test wells within the rotors. The rotors should be capable of separating relatively small volumes of blood and should not require the use of a displacement fluid for effecting such separation. In particular, it would be desirable to have a separation efficiency greater than 10%, preferably greater than 20%, and more preferably greater than 30%. The rotors should be able to accommodate relatively large numbers of test wells, and the rotor design should be simple and amenable to low-cost manufacturing procedures. In particular, it would be desirable if the rotors were of unitary construction with no separable or movable parts. Plasma separation methods should be simple and be capable of being performed in relatively short times. In particular, the methods should require relatively few steps and should be capable of being performed with little or no intervention or manipulations by the operator. It would be particularly desirable if the methods required only rotation of the rotor in order to effect both the separation and distribution of the plasma.
2. Description of the Background Art
U.S. Pat. No. 3,901,658, describes a centrifugal rotor which separates plasma from whole blood and transfers the plasma to a sample cuvette. The rotor requires use of a displacement liquid to force the plasma into the sample cuvette. U.S. Pat. No. 4,835,106, describes a centrifugal rotor which includes a plurality of removable capillary tubes for separating plasma from whole blood. The blood is introduced by placing a blood-filled capillary into a passage within the disk. U.S. Pat. Nos. 4,847,205 and 4,470,472, both describe centrifugal rotors which separate plasma from whole blood but which do not provide for in situ analysis. European patent application 160 282, discloses a test card which is used in a specialized centrifuge where a plurality of test cards are arranged annularly and where the cards may be rotated 90.degree. relative to the rotor to apply orthogonal forces to the card. The card must be turned (relative to the rotor) numerous times during a test cycle to effect a desired separation and plasma flow. The specialized centrifuge is described in U.S. Pat. Nos. 4,814,282; 4,776,832; 4,632,908, and European patent application 195 321. A system for two-dimensional centrifugation commercially available from KIS Photo Industrie, Gieres, France, is identified by the SATELIT tradename. The system uses a disposable test pack with a separable capillary collector for whole blood, as described in more detail in Truchaud et al. (1987), Clin. Chem. 33:1560. See also European patent application nos. 226 518; 251 946; 262 060, and French patent application 2 589 240. Other centrifugal rotor designs are described in U.S. Pat. Nos. 4,798,579; 3,707,354; 3,241,752; and 2,885,145.